In debating the question of chordate origins, zoologist eventually agreed that chordates must have evolved within the deuterostome assemblage rather than from a protostome group as earlier argued. What embryological evidences support this view?

Chordates share characteristics with deuterostomes such as: radial clevage, an anus derived from an opening of secondary origin, and a coelom primitively formed by fusion of enterocoelous pouches (except in vertebrates in which coelom formation is schizocoelus, but independently derived, as an accomodation for their large yolks).